The present invention relates to a system for determining the effective defibrillation energy discharged in an implantable defibrillation system without repeatedly inducing fibrillation of the patient's heart.
In the field of implantable defibrillation, it is well known that the energy level necessary for effecting defibrillation of a patient's heart varies with internal defibrillation lead configuration and placement, as well as the responsiveness of a particular patient's heart. It is necessary to determine, with the highest degree of accuracy, the minimal energy level necessary to defibrillate a patient's heart.
One known method to determine the defibrillation threshold energy of an implantable system is to induce fibrillation of a patient's heart. Once fibrillation is achieved, the heart is defibrillated through the implanted defibrillation leads. Initially, defibrillation is attempted at a relatively high energy level. If this energy level defibrillates the heart, the heart is placed in fibrillation again, and a defibrillation pulse of a lower energy level is applied to the heart. If this energy level defibrillates the heart, the process is repeated with lower defibrillation pulse energy levels until the heart is not defibrillated. Fibrillation-defibrillation episodes are often repeated at the lowest initially successful energy to obtain an estimate of that energy's probability for success, since an actual threshold does not exist. Finally, the defibrillation energy level for the permanently implanted device initially is set above that energy level which reliably defibrillated the heart, depending upon the decision of the physician.
A disadvantage of the above-described method is the need to repeatedly induce fibrillation of the heart, and to repeatedly defibrillate the heart to determine system thresholds.